1. Field of the Invention
The present invention relates to a liquid ejection head for ejecting a liquid such as an ink to conduct recording.
2. Description of the Related Art
An ink jet recording system is generally known as a recording system in which a liquid is ejected to conduct recording. This ink jet recording system includes a method utilizing a heating resistor element (heater) as an ejection energy-generating element used for ejecting a liquid such as an ink and a method utilizing a piezoelectric element (piezo). Both elements permit controlling the ejection of the liquid by an electric signal. In a recording head using the heating resistor element, thermal energy is applied to a liquid from the heating resistor element by supplying an electric pulse which is a recording signal to the heating resistor element to bring film boiling (bubbling) to the liquid. A bubble pressure generated at this time is utilized to eject the liquid from a minute opening, thereby conducting recording on a recording medium.
FIG. 5 is a partially broken perspective view illustrating a general construction of a liquid ejection head which is a recording head using the above-described heating resistor element. The liquid ejection head illustrated in FIG. 5 is equipped with a substrate 11 and an ejection orifice forming member 12 joined to one surface of the substrate 11. A through-hole as a liquid supply port 13 is formed in the substrate 11. A plurality of heating resistor elements 14 are arranged on both sides of an opening portion of the liquid supply port 13 on the surface of the substrates 11 to which the ejection orifice forming member 12 is joined.
In addition, FIG. 6A illustrates a plan view of the liquid ejection head when viewed from the side of the ejection orifice forming member 12. FIG. 6B illustrates a sectional view taken along line 6B-6B in FIG. 6A. As illustrated in FIGS. 6A and 6B, the ejection orifice forming member 12 is equipped with pressure chambers 15 arranged accordingly to the respective heating resistor elements 14, a plurality of liquid flow paths 17 for supplying a liquid such as an ink to the respective pressure chambers 15, a common liquid chamber 18 collectively communicating the plural liquid flow paths 17 with said one liquid supply port 13 and ejection orifices 19 communicating with the respective pressure chambers 15. The liquid flow paths 17, the common liquid chamber 18 and the ejection orifices 19 are formed of hollow portions such as grooves or holes formed in the surface of the ejection orifice forming member 12 on the side of the substrate 11.
Since the ejection orifice forming member 12 is equipped with the hollow portions such as the liquid flow paths 17 and the common liquid chamber 18, the member is a member brittle against external force. Therefore, a beam-like structure (hereinafter referred to as a beam 20) having a plurality of reinforcing ribs 20a is provided at a position of the common liquid chamber 18 facing the liquid supply port 13 in the ejection orifice forming member 12, thereby improving the rigidity of the ejection orifice forming member 12. The beam 20 and the reinforcing ribs 20a are formed in the form of a projecting line and brought into close contact with the substrate 11.
In addition, the reinforcing ribs 20a extend with a fixed thickness in the vicinity of an inlet of an optional liquid flow path 17 from the beam 20. At this time, the reinforcing ribs 20a are each formed on a line extending from a center line Y passing through a center of a flow path width d of the liquid flow path 17.
The fact that the beam 20 and the reinforcing ribs 20a are formed for improving the rigidity of the ejection orifice forming member 12 as described above is disclosed in Japanese Patent Application Laid-Open No. 2007-283501.
In the construction illustrated in FIGS. 6A and 6B, however, it has been found that when a bubble is generated in the vicinity of a side wall (hereinafter referred to as an end wall) on the side opposite to the liquid flow path 17 among side walls of the pressure chamber 15, the bubble is hard to be discharged from the pressure chamber 15.
A cause for this is as follows. Since a center line of the reinforcing rib 20a conforms to a center line Y of the liquid flow path 17 as understood from FIG. 6A, two gaps located between an end portion in a longitudinal direction of the reinforcing rib 20a and two side wall portions 17a of the liquid flow path 17 have the same size. In this case, liquid flows flowing toward the pressure chamber 15 from the two gaps through the liquid flow path 17 are flows having uniform velocity over the flow path width d of the liquid flow path 17. A bubble located in the vicinity of the end wall of the pressure chamber 15 is thereby pressed against the end wall and cannot be moved, so that there is a possibility that the bubble may stay in the pressure chamber for a long period of time.
In addition, the end portion in the longitudinal direction of the reinforcing rib 20a is arranged in the vicinity of the inlet of the liquid flow path 17, so that a flow resistance in the vicinity of the inlet of the liquid flow path 17 becomes high, and the force of the liquid flowing into the liquid flow path 17 becomes weak.
For the reason described above, the bubble generated in the vicinity of the end wall of the pressure chamber 15 is hard to be discharged from the pressure chamber 15. In addition, when the bubble stays in the pressure chamber 15, the growth of a bubble upon bubbling of the liquid is inhibited, and so stable bubbling cannot be conducted, and there is a possibility that ejection failure may be caused.